How big was Florida’s storm surge?

BIG PINE KEY — Heading down the Overseas Highway, past the growing piles of downed trees, ice chests, broken furniture, toppled signs and other debris that have turned the scenic drive into a long winding landfill, convoys of utility workers this week hurried toward the islands hardest hit by Hurricane Irma in a race to reconnect Conchs.

Barely noticed among them was a crew of six surveyors from the U.S. Geological Survey, racing to get in front of the cleanup.

Before homes and businesses are hosed down and aired out, and tedious rebuilding work begins, the crew needs to find and measure high water marks, the tiny traces of seaweed and sand that stick to walls, sign posts and anything left erect. Those marks provide the real-life evidence hurricane forecasters need to construct the powerful computer models used to issue warnings and keep people safe from a hurricane’s most lethal weapon: storm surge.

“In my 18 years here, I haven’t seen a peak surge where it was measured by an instrument,” said Jamie Rhome, who heads the National Hurricane Center’s storm surge team. “You have to figure it out by surveying the damage.”

In the days before Irma hit, forecasters warned that the massive storm was capable of generating surges across the state, from tip to toe. The Keys were expected to get between 5 and 10 feet. The hurricane had already become one of the most powerful on record, with 185 mph winds raging for 37 hours straight. When the storm curved west, tracking across the Lower Keys then winding up the Gulf Coast, forecasters weren’t far off.

Irma’s surge swept across the islands and up Biscayne Bay, inundating Miami Beach and downtown Miami. It dumped mud across Everglades City and other parts of Southwest Florida. The St. Johns River, far to the north, rose to record-breaking heights and flooded parts of Jacksonville. Where winds blew offshore from the counterclockwise spinning storm, bays were sucked dry, a powerful indicator of how bad the surge could have been if the storm had landed farther north. Buttonwood Bay in Key Largo and Tampa Bay briefly became beaches.

As the storm roared, tidal gauges that record water levels year-round and 130 temporary USGS sensors set out just before the storm began tracking the rising waters. But in monsters like Irma, instruments are prone to fail, leaving gaps in the data. A gauge near Tavernier stopped transmitting before noon Sept. 9. Of 500 gauges the USGS monitors in streams and rivers, 60 failed, said Richard Kane, associate director of the USGS’ Tampa-based Caribbean-Florida Water Science Center. And evacuation orders prevented crews from putting out sensors in the Keys, he said.

It will be several months before the hurricane center issues its comprehensive post-storm report that incorporates all kinds of data, Rhome said. But early measurements confirm that the Lower Keys and Southwest Florida met projections and got hit hardest, he said.

A USGS sensor in Manatee Bay south of Homestead showed water peaking at six feet, meaning the storm surge above ground level likely hit four feet, Kane said. Everglades City, a fishing village on the Southwest coast, saw a peak of eight feet, putting surges at about four to five feet, he said. Rhome said the surge in Jacksonville rose between three and five feet.

In Miami, seawalls kept the full volume of the surge from washing ashore. Flooding that turned Brickell Avenue into a river was more likely due to rain and waves topping the seawall, Rhome said.

“Brickell has a hard time with flooding during a rainstorm,” he said. “So there were a lot of things going on in the Brickell area that complicated flooding.”

For USGS hydrologic technicians Don Hampton and David Byers, finding the high water marks was a little like a treasure hunt, if the treasure was a needle buried in a jumble of hurricane debris.

Before dawn earlier this week, Hampton, who just returned from tracking Hurricane Harvey water marks south of Houston, and Byers, who spent the days leading up to Irma staking out temporary sensors, left their Key Largo hotel for Big Pine. Their descent into destruction gave them a good preview of what was to come in Big Pine, and a hurricane’s random kindness.

In Islamorada, the storm left the Lorelei’s giant mermaid untouched but shredded the Islander sign and battered its ocean-side cottages. Bud-n-Mary’s lost its sign. So did Lazy Days. On Pigeon Key, Irma knocked at least one cottage off its foundation.

Assessing water marks would not be easy. To start, Hampton and Byers needed to track down benchmarks, brass plaques in sidewalks or on buildings that have been embedded over the years to provide land surveyors, builders, engineers, map makers and scientists with precise locations and elevations. The benchmarks serve as a starting point, like the first hash on a measuring tape. A free app provides a map for the benchmarks, with a handy GPS locator attached.

Hampton and Byers can also access field notes that provide more information, including when the benchmarks were last visited. But the marks aren’t always where they’re supposed to be, Hampton said, and after a hurricane all bets are off.

Hampton and Byers are also looking for specific benchmarks: near canals where surge might have occurred and buildings, especially homes where residents might let them look inside. On Duval Street the day before, Byers said they lucked out and found high water marks on kiosks that seem perpetually open.

“Different surfaces collect different types of debris,” he said. “A stucco surface, if the right debris hits it, will stick nicely.”

In Big Pine, the app pointed them to a 1970 benchmark last checked in 1987. After some hunting around, they located it on a concrete step leading to a dock behind Strike Zone Charters near Mile Marker 29. It’s perfect. Just around the corner is Constitution Avenue, a street tucked between two canals and lined with mostly concrete stilt houses with stucco walls.

As they scouted the street in search of marks, Byers spotted what will turn out to be a major score: a yellow house halfway down the street, with a hole in its roof and an even line of seaweed — called a seedline — inside the downstairs carport.

Coming down the stairs on their way to buy building supplies were tenant Wayne Burri and his neighbor Ricky Moran.

Burri, who has tucked a shotgun by his front door, greeted Hampton and Byers with a storm-weary grimace, and led them to a downstairs utility room where he had already measured a water line between 22 and 25 inches from the floor.

“Everybody’s big question was was it nine feet here or two feet, and then you start measuring your appliances to see which ones hit the dust,” Burri said.

The small utility room, lined with over a dozen red gas containers, a rack of fishing rods and the washer and dryer, had created a perfect “stilling well” where water can rise without being influenced by waves that might make the surge appear higher.

Hampton and Byers spent the next couple of hours surveying the house and the street, pounding screwdrivers into the coral rock to mark their progress. Each step was noted in a shockproof, slightly waterproof laptop prone to overheating. It’s sweaty, tedious work that they repeat twice, for accuracy. They guzzled a half dozen bottles of water before entering the final water level for the utility room: 5.3 feet. Determining the actual surge level will take more calculations.

While he was surveying, Hampton had already started scouting what he thought might be a better spot on the ocean side of the highway, near the old Sea Center marina. In the 1960s, the marina sat at the center of the flats fishing world, where Tom McGuane, author of the Key West classic “Ninety-two in the Shade,” came to learn to be a fishing guide because it was the place to be “if you were besotted by this whole thing,” he later said.

Two-by-fours were nailed across the front plate-glass doors in what looks like a last-ditch effort to keep Irma out. About a half dozen center-console boats with powerful 225-horsepower motors that can sell for nearly $20,000 sit in a heap, a clear indication of strong surge. Three have been swept across the highway. As Hampton walked around the building, it became clear the place was now empty. Someone named Ron had scribbled on a plastic gate nailed to a side door “Monday 5 am.”

Then Byers hit the jackpot, discovering an especially poetic measure of Irma’s toll across the Keys.

Out by the highway, on a shelter erected by the National Park Service, he found a map box sheathed in plexiglass. There, preserved as if it were a lab specimen between the plastic and a map of the Overseas Heritage Trail, is a clear line of seaweed. It sits 3.5 feet above the raised asphalt trail, just below a red dot marking Higgs Beach in Key West, the end of the trail.

“You could easily drive by and not see that line if you’re not looking for it,” Hampton said. “You gotta be detectives sometimes.”

Once Hampton and Byers, and other field workers across the Keys and around the state, submit their field data, it will be verified and compiled with other information cataloged by scientists to calibrate models for more reliable predictions next time around. Unlike track models long used by forecasters to tell us where hurricanes go, surge models, and the warnings they generate, are still in their infancy.

“Storm surge was relatively forgotten, or it was off to the side and didn’t get much emphasis,” Rhome said. “Then Ike flooded Texas and caught people by surprise.”

The 2008 storm that killed 74 people in Texas alone sent a surge across Galveston at least 15 feet above ground level that flooded about 100,000 homes and forced nearly 3,000 people to be rescued from flood zones. Last year for the first time, the National Hurricane Center began issuing surge advisories to the public, using the SLOSH model that the National Weather Service began building in the 1990s. Florida International University and the University of North Carolina have also built surge models. Eventually, scientists hope to have a collection of surge models, similar to track models, that can create ensemble runs and more accurately predict surges. And the more their projections are verified in the field, the more reliable they become.

“This storm is going to be a big test, isn’t it?” said FIU coastal ecologist Stephen Leatherman, who helped design the university’s CEST model. “We don’t usually see Category 4 or 5 hurricanes hitting land.”

This story was originally published September 21, 2017 at 5:23 PM with the headline "How big was Florida’s storm surge?."